If you do some simple measurements on the picture of the shroud, you can see that the point where you assume the front and the back touch is not actually where you think it is. The point you are describing leaves considerably more cloth on the 'back' side. It also makes the distance between neck and top of the head much larger on the back side.

I think the latest evidence indicates that the shroud of Turin was a medieval prop used in Easter ritual plays depicting the resurrection of Christ and that it was used in a ceremony called the 'Quem Quaeritis?' or 'whom do you seek?' which involved re-enacting gospel accounts of the resurrection.
There are a number of theories. I don't think anyone will get to the bottom of it.